Project Summary/Abstract T cells are essential for immune surveillance since they recognize, attack and remove virus-infected and cancer-transformed cells. Inhibitory receptors (IR) temper inflammatory responses to microbial infections by regulating T cell effector activity. In humans, persistent viruses such as HIV, HCV and HBV as well as several types of cancer have adapted to exploit IR signaling by upregulating IR ligands, resulting in the suppression of T cell function (exhaustion) and escape from immune control. T cell exhaustion and the resurrection of T cell function, by neutralizing IR signaling, was first delineated in C57BL/6 mice following infection with the Clone 13 variant of lymphocytic choriomeningitis virus (LCMV). Infection with Clone 13 results in suboptimal CD4 and CD8 T cell effector function, ranging from reduced to absent cytotoxic capacity of CD8 T cells to decreased production of anti-viral cytokines such as IFN-? and TNF-?. Chronicling the resurrection of anti-viral T cell activity using antibodies that target IRs suggests that an in vitro phenotypic assay using the LCMV system could be an effective screening platform to identify novel small pharmacologic and beneficial molecule(s) that disrupt pathways regulating T cell dysfunction. To this end, we developed a screening strategy that utilizes transgenic mice (IFN-?-YFP) combined with high-throughput (HTS) flow cytometry to examine compounds that potentiate IFN-? expression in exhausted T cells isolated from LCMV infected animals. Using this approach, we propose to screen a best-in-class drug repurposing collection of 12,000 compounds (ReFrame) developed by TSRI?s non-profit affiliate, Calibr. The ReFrame library?s scale and comprehensiveness will allow us to explore complex biological processes in T cells and identify novel therapeutic agents that can reverse T cell exhaustion in the context of persistent viral infections and cancer.